Perhaps no other sub-specialty within immunology has advanced more rapidly in the past ten years than has the molecular characterization of cytokines and their receptors. Countless poorly defined soluble activities have now been shown to be associated with discrete gene products which function to control not only the development of immune reactivity, but the maintenance of all aspects of hematopoiesis as well. Attention has continued to focus on this field as many cytokines have been tested both preclinically and clinically and have been shown to manifest profound effects on restoration and maintenance of immune function in a host of clinical conditions. Recently, several of the genes which code for specific cytokine receptors have been identified. Through continued application of genetic engineering, soluble versions of several receptors have been produced and have been shown to modulate immune reactivity both in vitro and in vivo. Furthermore, elucidation of the structure of both cytokines and their receptors has opened this area of cell biology as an unequalled system in which to study the mechanisms behind signal transduction and the molecular control of growth and differentiation. Although recent activity surrounding cytokines and their receptors was the topic of isolated symposium at several major scientific meetings, no single symposium (save the International Lymphokine Workshop, which is held every three-years, alternately in Europe and the United States) is devoted to an in-depth review and discussion of the entire field from basic investigation through to examination of the effects of molecules in clinical studies. It is hoped that the proposed program would provide a unique forum in which investigators involved with all aspects of cytokine characterization and response - from biochemists concerned with mechanisms behind signal transduction, to cell biologists interested in the pathways of differentiation, to cellular immunologists focussed in the diversity and reactivity of immune response networks, to clinicians interested in manipulation of host immune reactivity in health and disease - can meet to discuss the intricacies and similarities behind cytokine dependent immune response pathways.